The present invention relates generally to a collet chuck assembly for holding a tool or workpiece on a spindle of a turning machine and particularly to a collet chuck that can be changed quickly and easily.
Collets are sleeves or collars used in various machine tools such as lathes for clamping or gripping workpieces or tools. Collets include a plurality of circumferentially-spaced, workpiece-gripping segments and conical surfaces or cams, which, when the collet is moved axially, interact with corresponding, opposing surfaces or cams on a mounting fixture or on the spindle. This interaction causes the workpiece-gripping segments of the collet to contract or expand to grasp or release a workpiece or tool, depending on the direction of movement. Collet chucks have commonly been used in machine tools in place of other types of chucks. Collet chucks are typically more accurate and have a greater gripping characteristic than a typical jaw chuck, for example. An advantage of collets is that they continue to grasp the workpiece or tool even at high rotational speeds when jaw chucks would have a tendency to loosen their grip due to centrifugal force.
One problem encountered with collet chucks is that slight variations in the diameter of the workpiece or stock could cause the collet to position the workpiece differently. When and where a collet will grasp a work piece depends on the difference in diameter between the open collet and the diameter of the workpiece. Precise workpiece diameter is therefore required if the workpiece is to be positioned precisely and consistently in machining operations such as facing, side finishing or cutting to precise lengths.
Another problem encountered with conventional collet assemblies is that collet cannot be easily and quickly removed from the spindle. Accordingly, changing collets can be time consuming.
For example U.S. Pat. Nos. 5,096,213 and 5,330,224, the respective disclosures of which are hereby incorporated by reference, disclose collet chucks in which a collet body includes an annular groove and hook portion on a rear end of the body which engages an annular flange portion of a spindle of the turning machine or a drawbar adapter of the collet assembly. A collet is installed by engaging the hook portion of the collet to the flange portion of the spindle or adapter, a special tool, such as those disclosed in U.S. Pat. Nos. 4,589,938 or 5,087,059, the respective disclosures of which are hereby incorporated by reference, is needed to compress the rear portions of the collet segments a sufficient distance radially inwardly so that the hook portion of the collet clears the annular flange portion. Similarly, to remove the collet from the turning machine, the tool must again be used to compress the rear portions of the segments so that the hook portions clear the flange portions so that the collet can be disengaged.